1. Field of the Invention
The present invention relates to the removal of fouling from the process lines of oil refining or petrochemical plants. More particularly, the present invention relates to a cleaning composition, which has excellent solvent strength against the fouling formed within oil refining or petrochemical process lines. Also, the present invention is concerned with a method for dislodging fouling using such a cleaning composition.
2. Description of the Prior Art
In oil-refining plants or petrochemical plants, fouling is one of the most problematic obstacles to their effective operation because it reduces the efficiency of heat exchangers and causes a large loss of energy as well as requiring frequent periodic maintenance for its removal. Typically, fouling results from deposits of crude petroleum, such as sand, silt and clay, corrosion of FeS, and heavy hydrocarbons, such as asphaltene.
In order to remove such fouling, various cleaning methods have been developed, along with cleaning agents. U.S. Pat. Nos. 4,773,357 and 5,006,304 disclose mechanical cleaning methods, in which a high velocity jet of water is applied to heat exchangers which are opened after the operation of the oil refining plant is ceased. In addition to costing a great deal of money in the cleaning of heat exchangers, such methods force the plant to submit to a serious loss because of the operation halt of the heat exchangers. Further, the opening of heat exchangers releases volatile organic compounds (VOC), producing pollution of the environment.
Chemical cleaning methods are referred to in U.S. Pat. Nos. 5,601,657 and 3,667,487. In general, chemical cleaning methods are based on the use of antifoulants. However, their poor cleaning efficiency per cost prevents applying the chemicals to entire oil refining processes.
U.S. Pat. No. 5,085,710 teaches the use of LCO (light cycle oil) having economical advantages over non-ionic surfactants or chemical cleaning agents in oil storage tanks so as to minimize the generation of sludge and to separate and recover hydrocarbons. The use of LCO as a cleaning agent is also referred to in Japanese Pat. Laid-Open No. Heisei 10-316997, in which 3-ethoxy propylene acid ethyl is used to remove a sludge and pollutants in heat exchangers without the problems of corrosion and waste water. Also Japanese Pat. Laid-open No. Heisei 6-126262 discloses that LCO is preheated to increase its solvent strength, and is used for the cleaning of heat exchangers.
For the cleaning of oil refining or petrochemical process lines, light gas oil (LGO) has recently been utilized. LGO is usually produced in a crude distillation unit (CDU). LGO is used as diesel or as a blending material for bunker C oil or kerosene. Since sufficient LGO is produced in CDU at low cost, and which can be readily utilized, LGO has been used with chemicals of 1 to 3 wt % added in the cleaning of process lines.
LGO and LCO are, however, a little bit inferior to expensive solvents such as toluene in solvent power, so they need the aid of other chemicals in cleaning process lines. However, the problems resulting from a poor solvent strength are not resolved in this method. Accordingly, there have been needs for more economical cleaning agents with good solvent strength.